A multi-center collaborative study to determine the sensitivity, specificity, positive predictive value and negative predictive value of contrast enhanced spiral computed tomography (spiral CT) for diagnosis of acute pulmonary embolism (PE). Pulmonary embolism is common, yet frequently undiagnosed and fatal. Ventilation/perfusion lung scans are the most commonly used test. However, they are non-diagnostic in 72% of patients with suspected PE and in 57% of patients with proven PE. Currently, Pulmonary Angiography is the definitive diagnostic test, but, there is hesitancy to use it because of morbidity, discomfort, discomfort, cost and lack of availability in community hospitals. Contrast enhanced spiral CT is a nearly non-invasive test that offers the possibility of a definitive diagnosis of PE by showing the outline of the thrombus in a pulmonary artery. However, its utility in the diagnosis of PE is unknown. Although spatial CT has not been adequately validated, physicians at many hospitals now use it as a definitive and only diagnostic test for PE, or as a definitive test in patients in whom the ventilation/perfusion lung scan is non-diagnostic. This could lead to over-treatment or under- treatment, of which, both have potential for serious complications. The role of spiral CT in the diagnosis of PE requires an accurate angiography. The strengths of this proposal are: 1) the importance of the problem of PE in terms of lives lost from under-diagnosis 2) the potential applicability of a new technology for the diagnosis of PE that will have widespread availability 3) the investigation team.